Water soluble azoformate esters

ABSTRACT

WHEREIN AT LEAST ONE OF R AND R&#39;&#39; CONTAINS A WATER SOLUBILIZING GROUP, SUCH AS 2-HYDROXYETHYL T-BUTYLAZOCARBOXYLATE WHICH ARE USEFUL AS POLYMERIZATION INITIATORS IN AQUEOUS MEDIUM FOR POLYMERIZAITION REACTIONS SUCH AS VINYL MONOMER POLYMERIZATION BY THE EMULSION TECHNIQUE.   R-OOC-N=N-R&#39;&#39; WATER SOLUBLE AZOFORMATE ESTERS OF THE FORMULA

United States Patent O 3,644,406 WATER SOLUBLE AZOFORMATE ESTERS Chester Stephen Sheppard, Tonawanda, and Ronald Edward MacLeay, Williamsville, N.Y., assignors to Pennwalt Corporation, Philadelphia, Pa. No Drawing. Filed Sept. 27, 1968, Ser. No. 763,342 Int. Cl. C07c 107/00, 107/02, 107/04 US. Cl. 260-192 Claims ABSTRACT OF THE DISCLOSURE Water soluble azoformate esters of the formula wherein at least one of R and R contains a water solubilizing group, such as 2-hydroxyethyl t-butylazocarboxylate which are useful as polymerization initiators in aqueous medium for polymerization reactions such as vinyl monomer polymerization by the emulsion technique.

BACKGROUND OF THE INVENTION (1) The field of the invention The invention relates to water soluble azoformate esters which are capable of affording free radicals. Also the invention relates to processes wherein these compounds are used to afford free radicals in an aqueous medium, e.g., emulsion polymerization of vinyl monomers.

(2) Description of the prior art Esters of azodiformic acid [ROC(O)N=NC(O)OR] are known. They have been used as dienophiles in Diels- Alder reactions, selective oxidizing agents, vulcanization agents (by allylic hydrogen additions to the azo-N=N- bonds), blowing agents for producing foamed polymers. and in various other chemical reactions. Only one reference is known wherein a polymerization initiator use is described. [E. I. Fedotova, R. Ya. Khvilivitskii, and I. I. Zmachinekaya, Uchenyl Zapiski Gorkovsk. Univ. 1953, No. 24, 183-9; CA. 50, 8461d' (1956).] Fedotova et al. used dimethyl azodiformate to polymerize methyl methacrylate in both bulk and emulsion polymerization systems.

In bulk polymerization systems, no water is present, and the free radicals required to initiate the polymerization must be generated in the organic (monomer) medium. In emulsion polymerization systems, water is present, and the free radicals must be generated in the water medium. Since Fedotova et al., used dimethyl azodiformate in both polymerization systems, it is not obvious from their work that Water soluble azodiformate esters will decompose in water to liberate free radicals. Fedotova et al. teach that dimethyl azodiformate decomposes thermally at 90 to 360 C. The water soluble azo esters of the present invention are not esters of azodiformic acid [ROC(O)N=NC(O)OR] but esters of azoformic acid (:R'N=N=C (0) OR) A Japanese patent [Japan 22743 (1963); CA. 60, 1909h 1964)] asserts that the disodium salt of azodiformic acid [NaOC(O) N=N-C(O)ONa] is an initiator for the emulsion polymerization of chloroprene and chloroprene copolymers at a pH above 8. Sodium salts are not esters and an azodiformate was used rather than the azoformates of the present invention.

3,644,406 Patented Feb. 22, 1972 ice The water soluble azoformate esters of the invention have the general formula:

where:

(a) R is a 1-7 carbon atom hydrocarbon radical or a substituted hydrocarbon radical having not more than 7 carbon atoms, the substituent is defined in (c);

(c) at least one of R and R contains a water solubilizing group selected from the class consisting of -OH, SO M, -OSO M,

(d) M is alkali metal, NH or H (e) Y is an n-valent inorganic acid anion;

(f) R and R are H, aliphatic, cycloaliphatic or aromatic;

(g) R and R are aliphatic or cycloaliphatic (h) R is aliphatic, cycloaliphatic or aromatic;

(i) R is hydrogen or lower alkyl;

(j) X is oxygen or sulfur;

0 0 r f I. I

and (1) R is the remainder of a heterocyclic ring.

The invention includes a process where free radicals are generated in an aqueous medium using as the free radical affording agent a water soluble azoformate ester as defined in I.

The invention also includes a process where solid polymer is produced by polymerizing vinyl monomer in an aqueous medium using free radicals as the polymerization initiator where the free radical affording agent is a water soluble azoformate ester as defined in L DESCRIPTION OF THE INVENTION AND WORKING EXAMPLES The compounds The novel azo compounds are defined in I supra. In the formula aliphatic and cycloaliphatic are used in their broadest technical meaning; however, it is to be understood that substituents which may be present in the aliphatic or cycloaliphatic radical must be inert to the azo function, so as not to interfere with the preparation reaction. Commonly the aliphatic radical will have 1-36 carbon atoms, usually 1-22, and the cycloaliphatic radical will have 3-12 ring carbon atoms, usually 4-8, in a single ring compound and 5-24 ring carbon atoms, usually 6-12, in a doubled or fused ring radical. It is to be understood that both aliphatic and cycloaliphatic may be substituted with aromatic group(s).

Aromatic is used in its broadest technical meaning and includes a single benzenoid ring, doubled (and higher) rings, and fused rings. These may be substituted with groups which are inert to the azo function or by one or more non-aromatic rings, including fused rings. Commonly these are phenyl, naphthyl and biphenyl radicals.

The above definitions are broad and intentionally so because the radical definitions of the compounds of Formula I do not affect the general utility of the compounds or the ability to make the compound by the processes set forth herein. Numerous compounds coming with Formula I are set out in the working examples.

A tertiary aliphatic radical is one Where the free valence is associated with a carbon atom which is joined directly through its other valences with three other carbon atoms, for example, a t-butyl radical.

Lower alkyl is intended to have about 1-12 carbon atoms and usually 1-8 carbon atoms, preferably 1-6 carbon atoms.

Alkyl, alkenyl, and alkynyl: Each alkyl group may include 1 or more carbon atoms. Desirably each has 1-22 carbon atoms. Preferably each has 1-12 carbon atoms.

Cycloalkyl and cycloalkenyl: May be single ring or have two or more fused rings. Desirably the single ring has in the ring 3-12 carbon atoms, and preferably 5-8 carbon atoms. Preferably the total number of carbon atoms in the radical is 5-12. Cyclopentyl, cyclohexyl, and the radical corresponding to Decalin are preferred radicals.

Aryl: May be a single benzene ring, or a doubled or higher system, e.g. biphenyl, terphenyl, quaternaphthalene, or a fused benzene ring system, e.g. naphthalene, anthracene, phenanthrene, or an alkane bridged system, e.g., biphenylmethane, biphenylpropane. Phenyl, biphenyl, naphthalyl and the alkyl substituted radicals are preferred.

Aralkyl: The Ar portion of the radical may be as in Aryl. The alkyl portion has desirably 1-12 carbon atoms and preferably 1-6 carbon atoms.

The preferred definitions of Rs R and R are H, alkyl, alkenyl, aralkyl, cycloalkyl, phenyl or naphthyl.

R and R are alkyl, alkenyl, aralkyl or cycloalkyl.

R is alkyl, alkenyl, aralkyl, cycloalkyl, phenyl, or naphthyl.

R is as R except for the carbon atom limitation.

It is to be understood that the above preferred definitions include the carbon atom limitations previously set out with respect to the various Rs.

Y is an inorganic anion. Anions derived from the mineral acids are preferred. Illustrative are F, Cl, Br-, HSO SO H PO HPO PO 5, ClO ClO CN, NO NO SO and C0 M is alkali metal. Illustrative are: Li, Na, and K.

The expression vinyl monomer includes all those organic compounds containing at least one CH :C group in their molecule. Examples of these monomers are styrene, alpha-methylstyrene, dichlorostyrene, vinyl naphthalene, vinyl phenol, acrylic acid and the alpha-alkyl substituted acrylic acids; the esters of these unsaturated acids, such as methyl acrylate, methyl methacrylate, butyl methacrylate, and propyl acrylate; the vinylidene halides, such as vinylidene chloride, vinylidene bromide and vinylidene fluoride; vinyl esters of the inorganic acids, such as the halogen acids and hydrocyanic acid, as vinyl chloride, vinyl bromide, acrylonitrile, and methacrylonitrile; the vinyl esters of the monocarboxylic acids, such as vinyl acetate, vinyl chloroacetate, vinyl benzoate, vinyl valerate, and vinyl caproate; the vinyl esters of the polycarboxylic acids, such as divinyl succinate, divinyl adipate, vinyl allyl phthalate, vinyl methallyl pimelate, and vinyl methyl glutarate; the vinyl esters of the unsaturated acids, such as vinyl acrylate, vinyl crotonate, and vinyl methacrylate; the vinyl ethers, such as vinyl ethyl ether, vinyl butyl ether, and vinyl allyl ether; the 'vinyl ketones, such as vinyl butyl ketone, and vinyl ethyl ketone; and the allyl derivatives, such as allyl acetate, allyl butyrate, diallyl phthalate, diallyl adipate, methallyl propionate, allyl 4 chloride, methallyl chloride, allyl acrylate, and methallyl methacrylate. The conjugated dienes, such as butadiene and chloroprene, are suitable.

These compounds are also effective as catalysts for the copolymerization of the above-described compounds with other types of polymerizable organic compounds, particularly those containing at least one ethylenic linkage; such as ethylene, the saturated esters of the unsaturated acids, such as diethyl maleate, dibutyl crotonate, and the like.

Using the novel azoformate esters of the present disclosure, ethyl acrylate Was polymerized in emulsion systems at relatively low temperatures using short reaction cycles. (Examples V to XXI.) The emulsion polymerizations can be carried out at temperatures ranging from below 0 C. to above 90 C. Generally, the range from 0 C. to about 80 C. is preferred. The amount of azoformate ester used can vary from about 0.05 to above 2.0 phr. Generally, 0.2 to 1.0 phr. is the preferred range. The use of more than one monomer to make copolymers is also applicable.

The pH range of the emulsion polymerization is not limiting except in those instances where the azoformate ester is more soluble in water at a certain pH range than another pH range. For example, 4-(ethoxycarbonylazo)- 4-cyanovaleric acid (Example I) is more Water soluble at pH of 8 and above than at lower pH, While isopropoxycarbonylazo-Nfl- 2'-pyridyl ethyl] formamide (Example II) is more water soluble in the lower pH range (i.e. below pH 7) than in the higher pH range. The emulsion polymerization results of Examples V and VI when compared to those of Examples VII-XI show that 4-(ethoxycarbonylazo)-4-cyanovaleric acid gives significantly higher polymer conversions in shorter times at pH of about 8 (sodium salt) than at pH of about 5 (free carboxylic acid). In this case the sodium salt is not only significantly more Water soluble than the free acid, it is also insoluble in the monomer, being only water soluble.

The results of Example XII when compared to those of Examples XIII-XV show that isopropoxycarbonylazo- N1E2-(2-pyridyl)ethyl]-formamide is more eflicient in the acid pH range than in the basic pH range. In this case, the pyridinium salt, which is formed in the acid pH range, is significantly more water soluble than the free base used in Example XII and again it is only soluble in water and not in the monomer.

The azoformate esters of Examples III and IV on the other hand are pH independent as far as their Water solubility is concerned. These products can be used in neutral emulsion polymerization systems, Whereas the azoformate of Example I gives best results in the basic pH range and that of Example II gives best results in the acid pH range.

Thus, azoformate esters of general structure I can be used in any pH range in emulsion polymerizations of vinyl monomers. Optimum initiator efliciency for any specific emulsion polymerization system can be readily obtained by selection of R and R.

In all other aspects, the conditions used for the emulsion polymerization systems (i.e. emulsifiers, water to monomer ratio, etc.) are typical of the established art.

Example XXII shows that azoformate esters without water solubilizing groups are not useful in emulsion polymerizations of vinyl monomers.

The azoformate esters of general structure I are also useful as gelling and/ or curing agents for Water extended resins (emulsified or dissolved in Water) that are nor mally gelled or cured by free radical generating initiators. (Example XXIII.)

In addition to their use in emulsion polymerizations, the azoformate esters of general structure I are useful in solution polymerizations of water soluble vinyl monomers such as acrylic acid, methacrylic acid, and the like.

The novel azoformate esters of general structure I can also be used for any other applications where the generation of free radicals in water are required, such as in freeradical catalyzed chemical reactions, and also for the generation of gases (i.e. nitrogen and carbon dioxide) from an aqueous system, such as in aerosol spray applications.

Although the present disclosure is not bound by theories, it is believed that the azoformate esters are first hydrolyzed to the unstable azoformic acid which then decomposes to liberate free radicals:

It is preferable in emulsion polymerizations that the azoforrnate ester be more water soluble than monomer (or oil) soluble since, if the reverse is true, the hydrolysis rate (and consequently the generation of free radicals) will be slower. However, this criterion is not always necessary. What is important is that the azoformate ester be substantially water soluble.

The major advantages of compounds of general structure I in aqueous polymerizations are the following:

(a) The azoformate esters are thermally stable compounds at ambient temperatures in the absence of water. Therefore, they can be easily shipped to fabricators without regard for refrigeration.

(b) In aqueous solution these compounds decompose at reasonable rates at room temperature thereby being capable of initiating polymerizations at room temperature or below.

(c) Since the hydrolysis occurs in the water phase, the radicals are generated completely in the water phase. This is an advantage in emulsion polymerizations over partially water soluble initiators which decompose thermally, and which also generate some of the radicals in the organic phase. This is detrimental to polymer properties in many emulsion polymerizations.

EXAMPLE I Preparation 4-(ethoxycarbonylazo)-4-cyanovaleric acid CH3 CZHBO iEN=N( JCHzOHQ( JOH A solution of 10.2 g. (.0875 m) of levulinic acid, 10.4 g. (0.1 m) ethyl carbazate and 4.9 g. (0.1 m) sodium cyanide in 50 ml. water was stirred for 2 days at room temperature. At the end of the 2 days the solution was transferred to a 250 m1. 4-neck round bottom flask and 50 ml. methylene chloride added. The mixture was cooled to 5 C. and 8.0 g. (0.1 m) of chlorine slowly passed into the mixture; holding the temperature below C. with an ice bath. The methylene chloride layer was separated, washed once with a saturated sodium chloride solution, dried over anhydrous sodium sulfate, filtered and the methylene chloride evaporated. The infrared spectrum of the resulting product was in agreement with that of the desired product. The product assayed 87.8% by an iodometric method. The yield was 83 EXAMPLE II Preparation of isopropoxycarbonylazo-N-[2-(2'- pyridyl ethyl] formamide To a solution of 9.6 g. (.0475 m) of diisopropyl azodicarboxylate in 50 m1. ethanol, cooled to --5 C., was added 4.88 g. (.040 m) of 2-(2-aminoethyl)pyridine dropwise over 15 minutes. The reaction was stirred an additional 15 minutes at 0 C. and filtered. The filtrate was poured into 100 ml. water and the resulting solution was extracted with 50 ml. pentane to remove the unreacted diisopropyl azodicarboxylic (2.45 g.). The aqueous solution was extracted with 100 ml. CH Cl the Ch Cl solution dried, filtered and the CH Cl evaporated leaving 9.9 g. of a viscous paste. The paste was slurried in 50 ml. ether, the mixture cooled to -20 C. and filtered. The filter cake weighed 2.05 g. and was azodicarbonamide. The ether filtrate was stripped to constant weight leaving a dark orange-red liquid weighing 6.55 g. (62.7% yield). The infrared spectrum of the liquid was in agree ment with that of the desired product.

The pyridyl compound B above is readily converted to its inorganic acid salt. These salts have the empirical formula l -HlflYl where: n equals the valence of the inorganic acid anion Y. Illustrative of these salts are:

[B-Hl Cl- Preparation of isoproxycarbonylazo-N-(2-hydroxyethyl) formamide To a solution of 9.6 g. .0475 m) of diisopropyl azodicarboxylate in 50 ml. of ethanol, cooled to 5 C., was added 3.0 g. (.049 m) of ethanolamine. Precipitation of an orange solid slowly occurred after the addition was complete. The reaction was stirred an additional 15 minutes at 5 C. and filtered. The filter cake was azobis- [N-(2-hydroxyethyl)formarnide] and was discarded. The ethanol filtrate was stripped to dryness leaving 9.3 g. of a solid suspended in a liquid. This material was slurried in pentane 3 times and the pentane decanted off and discarded. This contained the unreacted diisopropyl azodicarboxylate (1.6 g.). The residue was slurried in 50 ml. methylene chloride and filtered. The filter cake weighed 0.8 g. and was more azobis-[N-(2-hydroxyethyl)formamide]. The methylene chloride solution was stripped to dryness leaving 5.2 g. (53 /2 of a blood red liquid. The infrared spectrum of the product is in agreement with that of the desired product. The material is water soluble. It assayed by iodometric titration.

EXAMPLE IV Preparation of 2-hydroxyethyl t-butylazocarboxylate Into a ml. round bottom flask was weighed 22.0 g. (.25 m) of ethylene carbonate and 27.0 g. (.25 m) of 80% t-butylhydrazine. The mixture was heated in an oil bath at 70 C. for 7 hours and allowed to cool overnight. An infrared spectrum of the material confirmed that all the ethylene carbonate had reacted and the spectrum was in agreement with the structure of 2-hydroxyethyl t-butylhydrazocarboxylate. The product weighed 47.75 g. but contained about 5 g. of water. The purity of the hydrazo was 89.5%.

Into a 100 ml. 4 neck round bottom fiask was weighed 10 g. (.506 m) of the above hydrazo and 25 ml. of water and 25 ml. of methylene chloride were added. The mixture was cooled to 5 C. in an ice bath and chlorine passed into the mixture at 0.2 g./min. until 3.90 g. (.549 m) were absorbed. The reaction was stirred an additional 10 minutes, the CH Cl layer separated, Washed once with 10 I ml. water, twice with 10 ml. 10% NaHCO solution and once with saturated salt solution. The CH Cl solution was dried over anhydrous Na SO filtered, and the CH Cl stripped otf. The yield was 6.3 g. (75%) of a yellow 3. liquid which assayed 87% by iodometric analysis. The in- M H NflN ll H OH frared spectrum was in agreement with the structure of 2 QOCT C N 920 S hydroxyethyl t-butylazocarboxylate. 0

EXAMPLES V XXIH 5 MeOgN=N1NII(CII:)2O s 03H Emulsion polymerization of ethyl acrylate with f H azo esters iO;H1OCN=NCNlI(OH2) C0Na,

A mixture of 50 g. of ethyl acrylate, 40 g. water and u. 0 6 g. Triton X200 emulsifying agent was placed in a 4 neck g g OaNa round bottom flask equipped w1th a water cooled coudenser, a thermometer, a self-venting addition funnel, tub- H ing for the continuous flushing of the system with nitrogen, m s 03H and a mechanical stirrer. The mlxture was warmed up to the desired reaction temperature in a constant tempera- H ture bath (see Table I). The desired initiator was then t-C H\1N:N-C-O(CHzCHzOMH weighed into 10 ml. water. [In Examples VII-XI a molar equivalent of sodium bicarbonate was added to the water 9 H to convert the 4-(ethoxycarbonylazo)-4-cyanovaleric acid I -GN:N-C O(CH2)3N(CH;)3I9 to its sodium salt. In Examples XIII-XV a molar equiv- H3 alent of sulfuric acid was added to the water to convert the isopropoxycarbonylazo N 2(2'-pyridy1ethyl)form- F f amide to the pyridinium salt.] The aqueous solution of the 1n1t1ator was then added to the reaction flask. The polym- Cl erization was carred out for the indicated time (Table I). Aliquots of the emulsion were taken, the water and 11, 0411 0 ii unreacted monomer allowed to evaporate, the residue CH3 C N:N COCH? CH2OH weighed and the percent conversion to poly(ethylacrylate) determined. CN

TABLE I Initiator eonc. (gm/100 g. Temp., Time Percent; Example Initiator monomer) degree (hrs) conv.

V t. 4-(ethoxycarbonylazo)-4-cyanovaleric acid 1.0 25 3 2.5 VI.-. o 1.0 2% VII. Sodium 4-(ethoxyearbonylazo)-4-eyanovalcrate. 1. 0 25 2% 49 VIII- 1.0 40 IX do. 1.0 50 1 74 X A0. 1.0 50 a XI d0 A 1.0 60 85 XII IsopropoxyearbonyIazo-N-2(2-pyridylethyl)- 1.0 50 6 2O iormamide. XIII Isopropoxycarbonylazo-N z(2-pyridylothy1)- 1.0 25-60 3f; 88

formamide hydrogen sulfate. XIV -do 1.0 50 1% 75 XV do 1.0 60 62.5 Isopropoxycarbonylazo-N-(Z-hydroxyethyl) l. 0 25 3 42 iormamide.

EXAMPLE XXIII H 12 PM 0 2-hydroxyethyl t-butylazocarboxylate (from Example c1-I :-N=N( io(ClIzCiI 0 ,,H IV) was used to catalyze a commerclal water extended resin (AROPOL WEP, an unsaturated polyester resina styrene blend by Ashland Oil & Refining Co. formulated r 1.5. O to be extended with water to form a water-ln-oil emulsion H with the formulation used in this test containing about I S |-N=N--'C 60% water) at 25 C. in an amount corresponding to one 091.13 percent by weight of the resin. The resin completely (IJMO gelled in 10 minutes. When the test was conducted at 82 T C. F), the resin gelled in 5 minutes and cured in Gr 2 6.3 minutes. Without the azo compound, the resin does 0 CH2 not gel or cure at 82 C. (180 F.). Other compounds which come within the scope of this invention are: Me=methyl; Et=ethyl; I =phenyl; Na Pr=propyl; and Bu=butyl P ll iC H OCN=NCNH(CH CHzO)H S COCHPCEOH EtOCN:N-CN[(CHZCHzO) H1 75 ('JH Compound 16-34 have a common structural formula:

CH3 EtO( ]N=N-( JCH2CHz C ONa where Z is:

CfiQCH- 18. n-BuS- t-BuO 0- 20. NH E40 L HzNPk- 28. O Emb- Eu) S- EtOPJS- Eta-( s- 1. An azoformate ester of the formula:

10 where: (a) R is an alkyl radical having 1-6 carbons;

R1 is (|-I1IR2 or (il-R4 (c) at least one of R and R contains a water solubilizing group selected from OH, SO M, OSOgM,

11 I [N(R1)a]n Y', o OM and -(CHz-OHO) --H (d) M is alkali metal, NH or H (e) Y is an n-valent inorganic acid anion;

(f) R R and R are alkyl, alkenyl or alkynyl of l-22 carbons; cycloalkyl or cycloalkenyl of 3-12 carbons; phenyl; biphenyl; or naphthyl; and R and R can also be H;

(g) R and R are alkyl, alkenyl or alkynyl of 1-22 carbons; cycloalkyl or cycloalkenyl of 3-12 carbons; and together can form an alkylene diradical of 4-5 carbons;

(h) R is hydrogen or alkyl of l-6 carbons;

(i) X is oxygen or sulfur;

n 1? 1 u i CORs, OOOIh, C-ORa, cl-NHz, C-N-R; X x II I! -XO-Rr 01'--X--C--OR;

and (k) n is 1-3.

2. Claim 1 where R is a ?-RI i r 0 CzH O CN=NOGH2OH2O OM where M is alkali metal, NH or H+.

I. i? r i-CaHrO G--N=N-C-N-CH2CH2OH (OHs)aCN=N- l0 CHaCHrOH References Cited UNITED STATES PATENTS 2,903,361 9/1959 Marks et a1. 260-192 X 3,282,912 11/1966 Benzing 260-19-2 X 3,474,085 10/1969 MacLeay et a1 260-192 3,522,233 7/1970 Sheppard et a1. 260-192 FLOYD D. HIGEL, Primary Examiner US. Cl. X.R.

252-426; 260-29.6 R, R, 86.1, 88.7 R, 91.5, 92.8 R, 92.8 W, 93.5 R 

